TECHNICAL FIELD

The present invention relates to dairy products. I n particular, the invention is concerned with milk powder compositions comprising a protein complex which contributes to the improvement of creaminess, mouthfeel and texture, in particular of products based on lower and no fat formulations. A method of producing such milk powder products and the products obtainable from the method are also part of the present invention. BACKGROUND OF THE INVENTION

Powdered milk or dried milk is a manufactured dairy product made by evaporating milk to dryness. It involves the gentle removal of water at the lowest possible cost under stringent hygiene conditions while retaining all the desirable natural properties of the milk - color, flavor, solubility, nutritional value. Whole (full cream) milk contains, typically, about 87% water and skim milk contains about 91% water. During milk powder manufacture, this water is removed by boiling the milk under reduced pressure at low temperature in a process known as evaporation. The resulting concentrated milk is then sprayed in a fine mist into hot air to remove further moisture and so give a powder.

Powdered milk is usually made by spray drying non-fat skimmed milk, whole milk, buttermilk or whey. Pasteurized milk is first concentrated in a n eva porator to approximately 50% milk solids. The resulting concentrated milk is then sprayed into a heated chamber where the water almost instantly evaporates, leaving fine particles of powdered milk solids.

Spray-draying of a milk composition is described, for instance, in US 5,350,590.

Mouthfeel and creaminess as well as lower or reduced fat are key drivers of consumer liking for dairy products such as coffee mixes or coffee enhancers as well as a high number of other products.

Today, there is a challenge to either increase or retain the mouthfeel/creaminess of powders when fat is reduced or removed. Thus the objective of the present invention is to use all-natural formulation or ideally by the product matrix itself, instead of adding ingredients to the product, particularly in low and no fat products.

It is known since 1980's that a slight pH adjustment of native fresh milk prior to heat treatment results in change of aggregation behavior between casein micelles and whey proteins. However, the pH ra nge that was explored in milk never went down lower than pH 6.3 [F. Guyomarc'h. 2006. Formation of heat-induced protein aggregates in milk as a means to recover the whey protein fraction in cheese manufacture, and potential of heat-treating milk at alkaline pH values in order to keep its rennet coagulation properties. A review. Le Lait, INRA Editions, 86(l):l-20.]

Adding thickeners (e.g. hydrocolloids, starches) has shown no big success due to unexpected texture change, flavor loss, increased length of ingredient list and also increased formulation costs.

EP0333288 relates to spray dried milk powder product and process for its preparation. It was found that a spray dried whole-milk powder with a coarser fat dispersion can be prepared by causing the spraying to be effected in such conditions that a considerable portion of the fat in the pre-concentrated milk product to be dried is in the solid state.

EP1127494 relates to a process for the preparation of fat-containing milk powder. US6541056 relates to a malted beverage powder and a process for preparing it, in which liquid beverage ingredients and a first portion of dry malted beverage ingredients are wet mixed to provide a wet mixture having a moisture content of about 20% or less. The wet mixture is vacuum dried to provide a dry cake which is comminuted to a base powder. The base powder is then dry mixed with a further portion of dry malted beverage ingredients. The malted beverage powder so obtained has a substantially homogeneous colour and characteristics such as flavour and texture similar to those of conventionally-prepared malted beverage powder.

GB 345,302 relates to improvements in drying apparatus, in particular for drying milk, so that the resulting powdered milk may be kept without deterioration for a considerable period. Milk may be dried on band conveyors arranged within a vacuum chamber, where each of the ban conveyors passes over a series of hot plates. Then, the solid milk is ground still under vacuum.

Taterka and Castillo (2015) "The effect of whey protein denaturation on light backscatter and particle size of the casein micelle as a function of pH and heat-treatment temperature" Int. Dairy J. 48:53-59, disclose several pH and heat treatments of reconstituted skim milk.

Thus it is an object of the present invention to improve the mouthfeel, texture, thickness, or creaminess of the current products in the market. It is also an object of the present invention to keep mouthfeel/texture/thickness/creaminess of a product constant while reducing fat content. Furthermore it is also an object of the present invention to keep the mouthfeel, texture, thickness, or creaminess of a product constant while reducing or eliminating thickening agents/stabilizers, e.g. hydrocolloids or starch.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the state of the art, and in particular to provide a process that overcomes the problems of the prior art and addresses the needs described above, or at least to provide a useful alternative. In particular, it is an object of the present invention to provide a process to manufacture a milk powder that provides protection against loss of structure and function of aggregated proteins.

It was surprisingly found that through control of pH, the whey proteins in combination of controlled heat treatment (temperature and hold time) form complexes with the casein micelles, which results in increased colloidal particle size, water binding and overall viscosity.

Accordingly, an embodiment of the invention proposes a process for preparing a milk powder, said process comprising the steps of:

(a) Providing a milk concentrate having a total solids content of about 50-65 % at a temperature below 40°C;

(b) Adjusting pH to 5.9 and 6.5 ;

(c) Vacuum drying the milk concentrate to provide a dry cake;

(d) Cooling the dry cake; and

(e) Comminuting the dry cake to a powder.

Another embodiment of the invention is a milk powder comprising caseins and whey protein wherein the powder upon reconstitution in an aqueous medium comprises caseins and whey protein/fat aggregates having a mean diameter value Dv50 of at least 1 μιτι as measured by laser diffraction, wherein the milk powder is obtainable by a process as mentioned above.

Another embodiment of the invention is the use of the milk powder for producing a powdered growing-up milk, a powdered culinary sauce, a powdered coffee mix, a powdered coffee or tea creamer, or a powdered cocoa-malt beverage These and other aspects, features and advantages of the invention will become more apparent to those skilled in the art from the detailed description of embodiments of the invention, in connection with the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows light microscopy images of milk powders reconstituted in water. A: Reference milk powder (see example 1). B: sample 1 of the present invention (see example 1). C: sample 2 of the present invention (see example 1). Scale bars are 50 microns.

Figure 2 shows particle size distributions of vacuum dried powders according to reference (A) and samples of the present invention (B and C) as explained in Example 2.

Figure 3 shows pictures to illustrate the consistency of wet mixtures obtained by mixing skim milk powder with water, at various total solids contents.

Figure 4 shows a bar diagram comparing Sa mple 1 and the Reference of Exampole 1. A = Body; B = Smooth; C = Mouth coating; D = Overall Flavour; E = Dairy; F = Sweet; G = Other Flavour; H = Lasting. Bars with a squared grid a re significantly different from the reference. White bars are not significantly different from the reference. ANOVA: 95% confidence level.

DETAILED DESCRIPTION OF THE INVENTION

As used in the specification, the words "comprise", "comprising" and the like are to be construed in an inclusive sense, that is to say, in the sense of "including, but not limited to", as opposed to an exclusive or exhaustive sense.

As used in the specification, the word "about" should be understood to apply to each bound in a range of numerals. Moreover, all numerical ranges should be understood to include each whole integer within the range.

Unless noted otherwise, all percentages in the specification refer to weight percent, where applicable.

Unless defined otherwise, all technical and scientific terms have and should be given the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As mentioned above, an embodiment of the invention relates to a milk powder comprising caseins and whey protein wherein the powder upon reconstitution in an aqueous medium comprises caseins and whey protein/fat aggregates having a mean diameter value The term "particles having mean diameter value Dv50" refers to protein network comprising casein micelles and whey proteins either present in aggregates.

The mean diameter value Dv50 of the milk powder of the present invention ranges from 1 μιτι - 120 μιτι. Preferably, the mean diameter Dv50 ranges from 50 μιτι to 100 μιτι. The method for measuring the mean diameter Dv50 is explained in Example 2.

The term "upon reconstitution in an aqueous medium" refers to reconstituting the milk powder into a liquid such as water. The liquid may be milk. Such a process is carried out typically at room temperature and may involve stirring means. The process may be carried out at elevated temperature, e.g. 85°C for a hot beverage preparation.

It has surprisingly been found that texture and mouthfeel of dried milk powder is enhanced as a result of an optimized process of preparation including the controlled use of heat and acidic conditions.

These protein aggregates form a network that is suspected of binding water and entrapping fat globules (in case of presence of fat) and increases mix viscosity to create a uniquely smooth, creamy texture that mimics the presence of higher fat levels.

In one embodiment of the present invention, the vacuum-dried milk composition does not include any thickeners and/or stabilisers. Examples of such thickeners include hydrocolloids, e.g. xanthan gum, carrageenans, guar gum, locust bean gum or pectins as well as food grade starches or maltodextrins.

In one embodiment the milk powder of the present invention is used in producing a powdered growing-up milk, a powdered culinary sauce, a powdered coffee mix, a powdered coffee or tea creamer, or a powdered cocoa-malt beverage.

The milk power may be prepared from skim milk, semi-skim milk or full fat milk. The milk powder may be lactose-free. For instance, the milk powder is prepared from milk concentrate having a total solids content of about 50 to 65%. Alternatively, the milk powder is prepared from a wet mixture which is obtained by mixing a standard milk powder with water, to provide a mixture having a total solids content of about 50-65%.

The term "standard milk powder" refers to a milk powder which was manufactured from milk without pH adjustment during manufacturing. For instance, it may be a commercial spray-dried milk powder. The milk used in the manufacture of standard milk powder may be raw or standardised milk. In some instances, lactose is removed from the milk by conventiona l methods. In some instance, the milk is homogenised before spray-drying. In one embodiment, the present invention also relates to a process for preparing a milk powder comprising the steps of:

a) Providing a milk concentrate having a total solids content of about 50-65 %;

b) Adjusting pH to 5.9 and 6.5;

c) Vacuum drying the wet mixture to provide a dry cake;

d) Cooling the dry cake; and

e) Comminuting the dry cake to a powder.

As already mentioned, the milk concentrate may be prepared by mixing milk powder to provide a wet mixture having a total solids content of about 50-65%. Accordingly, in an embodiment, the present invention relates to a process for preparing a milk powder comprising the steps of:

a) Mixing milk powder (i.e. standard milk powder) with water to provide a wet mixture having a total solids content of about 50-65%;

b) Adjusting pH to 5.9 and 6.5;

c) Vacuum drying the wet mixture to provide a dry cake;

d) Cooling the dry cake; and

e) Comminuting the dry cake to a powder.

In this case, the milk powder is selected from skim milk powder, semi-skim milk powder and full fat milk powder. Figure 3 shows the consistency of wet mixtures obtained by mixing skim milk powder in water, at several total solid contents. The consistency of the wet mixture on Figure 3a is too liquid. Vacuum drying it is very difficult. The consistency of the wet mixture on Figure 3d is too dry or doughy. It is not possible to distribute it on the belt of a vacuum belt dryer. The ideal consistency is illustrated on Figures 3b and 3c, where the wet mixture is pasty or a thick liquid. In this case, it is rather easy to distribute the wet mixture on the belt of a vacuum belt dryer, and to dry it.

The inventors have found that in order to reach the ideal consistency, the target total solids content of the wet mixtures depends on the fat content of the milk powder. For instance, when the milk powder is skim milk powder, the target total solids content of the wet mixture ranges from 55 to 60%, as shown on Figure 3. When the milk powder is full fat milk powder, the target total solids content of the wet mixture rather ranges from 60 to 65% in order to reach the desired consistency.

The pH of the milk concentrate, or of the wet mixture, is adjusted to 5.9 to 6.5. Preferably, it is adjusted to a pH of 6.0 to 6.4, or preferably to a pH of 6.0 to 6.3. This may be performed by adding a food-grade alkali or a food grade acid, depending on the starting point. For instance, the pH of the wet mixture is adjusted using a food-grade alkali, such as NaOH.

Preferably, the process is performed in a continuous manner, especially between steps (b) and (c). Indeed, due to the high total solids contents, lactose may crystallise in the wet mixture, if a too long time elapses between steps (b) and (c). Alternatively, lactose-free milk is used. In this context, "continuous" shall mean that the manufacturing set-up is such that lactose crystallisation does not occur significantly between steps (b) and (c) of the process, i.e. if lactose crystallisation occurs, it does not hinder the usual operation of the vacuum belt drier.

The drying of the milk concentrate, or of the wet mixture, is carried out in a vacuum band drier which is able to handle extremely viscous mixtures. Vacuum band driers are particularly preferred. Conventional vacuum band driers are particularly suitable. Using a vacuum drier, the mixture is dried to a cake. Typical vacuum drying conditions may be used, for example, temperatures ranging from about 120°C to about 160°C and pressures ranging from about 0 bar to about 100 mbar, preferably from about 20 mbar to about 50 mbar.

The residence time in the vacuum belt drier ranges from 20 to 60 minutes, depending on the water content of the milk concentrate or the wet mixture, on the temperature in the vacuum belt drier, and on the pressure. For instance, when the vacuum belt drier is operated at about 130°C at a pressure of about 25 mbar, the residence time of a wet mixture comprising 55% total solids is about 45 minutes. Also for instance, a wet mixture comprising 65% total solids may be dried in a vacuum belt drier in 25 minutes at about 155°C at a pressure of about 25 mbar.

The cake which is about to leave the vacuum drier may be cooled before leaving the drier. Alternatively it may be cooled after leaving the drier.

At this stage, the cake is dry. The term "dry cake" means that cake contains less than about 5% by weight of moisture, preferably less than about 4% by weight of moisture, and most preferably less than about 3% by weight of moisture.

The dry cake is then comminuted using one or more crushers or mills as necessary. Particles are sieved through a 250 micron sieve. The powder obtained comprises less than about 5% by weight of moisture, preferably less than about 4% by weight of moisture, and most preferably less than about 3% by weight of moisture. I n particular, the process achieves a milk powder which, when reconstituted in aqueous medium results, in casein-whey protein aggregates having a mean diameter value Dv50 ranging from 1 - 120 μιη.

It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention.

The invention will now be described in further details in the following non-limiting examples. Further advantages and features of the present invention are apparent from the figures and non-limiting examples. EXAMPLES

Example 1

Reference 1

This reference represents a standard lactose free skimmed milk powder purchased from Valio Ltd. containing protein 45% and fat 1.5%. Process conditions are unknown.

Sample 1 of present invention

Lactose-free skimmed milk powder (protein 45%; fat 1.5%) is reconstituted with water in a Stephan mixer to provide a milk concentration of 55% total solids. The milk concentrate is adjusted to pH 6.2 using 32% NaOH.

The milk concentrate is transferred to a vacuum band drier which is operated at about

130°C, at about 25mbar. The vacuum band drier includes a cooling stage operated at 30°C. The residence time in the vacuum belt drier is about 60 minutes. The cake leaving the vacuum belt drier has a moisture content of a bout 5%. The cake is then crushed and milled to a particle size of <250 microns.

Sample 2 of present invention

Lactose-free skimmed milk powder (protein 45%; fat 1.5%) is reconstituted with water in a Stephan mixer to provide a milk concentration of 55% total solids. The pH of the milk concentrate is measured to be pH 6.

The milk concentrate is transferred to a vacuum band drier which is operated at about

130°C, at about 25mbar. The vacuum band drier includes a cooling stage operated at 30°C. The residence time in the vacuum belt drier is about 45 minutes. The cake leaving the vacuum belt drier has a moisture content of about 5%. The cake is then crushed and milled to a particle size of <250 microns.

Sample 3 of present invention

Skimmed milk powder (protein 34%; fat 1.5%) may be reconstituted with water in a twin-screw mixer or a Stephan mixer to provide a milk concentration of 60% total solids. The milk concentrate may then be adjusted to pH 6.2 using 32% NaOH.

The milk concentrate may be transferred continuously to a vacuum band drier which is operated at about 130°C, at about 25mbar. The vacuum band drier includes a cooling stage operated at 30°C. The residence time in the vacuum belt drier is about 45minutes. The cake leaving the vacuum belt drier has a moisture content of about 5%. The cake is then crushed and milled to a particle size of <250 microns.

Sample 4 of present invention

Full fat milk powder (protein 34%; fat 28%) may be reconstituted with water in a twin- screw mixer or a Stephan mixer to provide a milk concentration of 65% total solids. The milk concentrate may then be adjusted to pH 6.5 using 32% NaOH.

The milk concentrate may be transferred continuously to a vacuum band drier which is operated at about 155°C, at about 25mbar. The vacuum band drier includes a cooling stage operated at 30°C. The residence time in the vacuum belt drier is about 25minutes. The cake leaving the vacuum belt drier has a moisture content of about 5%. The cake is then crushed and milled to a particle size of <250 microns.

Example 2 - Physical Properties

Microstructure of the reconstituted powders

The reconstituted powders of the reference (A in Figure 1) and samples 1 (B in Figure 1) and 2 (C in Figure 1) of the invention have been investigated by light microscopy. Powdered samples were reconstituted before measurements. 87.5ml of distilled water was poured into a breaker. Using a magnetic stirrer, 12.5g of sample was dosed slowly into the beaker and mixed for 30 minutes at 350rpm.

An Olympus SZX9 Stereomicroscope coupled with an Olympus DP21 camera was used. The systems were observed under bright field. An aliquot of 500 microliters of liquid sample was deposited on a glass slide and covered with a cover slide before observation under the microscope. Results are shown in Figure 1.

Samples of the present invention shows controlled aggregate formation which is a microscopy signature of protein complex formation at molecular scale.

Size distribution measurements

The milk powders of the present invention were compared to the above reference and were characterized by laser diffraction in order to determine particle size distribution (PSD =

Particle Size Distribution).

Results are shown in Table 1 below wherein the PSD measured by laser diffraction represents a mean value Dv50 (μιη).

The size of particles, expressed in micrometers (μιη) at 50% cumulative distribution

(Dv50) was measured using Malvern Mastersizer 2000 (laser diffraction unit). Ultra-pure water was prepared using Merck Milli-Q. Integral water Purification System. Powdered samples were reconstituted before measurements. 87.5ml of distilled water was poured into a breaker.

Using a magnetic stirrer, 12.5g of sample was dosed slowly into the beaker and mixed for 30 minutes at 350rpm.

Measurement settings used are a refractive index of 1.46 for fat droplets and 1.33 for water at an absorption of 0.01. All samples were measured at an obscuration rate of 2.0-2.5%.

The measurement results are calculated in the Malvern software based on Mie theory.

The resulting Dv50 obtained for the 3 samples are presented in table 1.

Figure 2 shows particle size distributions of vacuum dried powders according to reference (A) and samples of the present invention (B and C). It is clear that for the vacuum dried milk powders of the invention, the Dv50 was at least 1 micron.

Table 1: Dv50 (in microns) of reconstituted powders as determined by laser diffraction.

Although the invention has been described by way of example, it should be appreciated that variations and modifications may be made without departing from the scope of the invention as defined in the claims. Flow behaviour of the reconstituted powders

After reconstitution to 13% total solids in water at 25°C. The milk powders of the present invention were compared to the above reference and were characterized using an AR 2000 ex Rheometer (TA instruments), coupled with a temperature control Thermocube chiller, regulating to 25±0.1°C. The measuring geometry was a cup and bob system, at a measuring gap of 5920μιη.

The flow curve was obtained by applying a controlled shear stress to a 12-15ml sample in order to cover a shear rate range between 0 to 100 1/s (controlled rate linear increase). From the flow curves, the shear viscosities corresponding to a shear rate of 100 1/s were determined. The viscosity ratio was calculated and reported in Table 2.

Table 2: Rheological properties determined at 25°C for VBD-dried powders reconstituted at 13% total solids.

This shows that the treatment performed on sample 1 increases the viscosity of the reconstituted milk product. This will bring more mouthfeel and coating to the product with a protein level similar to that of non-treated milk.

Example 3 - Sensory Characteristics

Sample preparation for 600ml final beverage was 90g powder, filled up to 600ml water. The serving temperature was 50°C. The panellists were asked to rate the sample 1 (example 1) in the following attributes, to a blind version of reference (Example 1): A = Body; B = Smooth; C = Mouth coating; D = Overall Flavour; E = Dairy; F = Sweet; G = Other Flavour; H = Lasting

The results are shown in Figure 4, where the sample was perceived to have significantly more body, overall flavour, sweetness and other flavours than the reference. ANOVA: 95% confidence level.

In figure 4, the bars with a squared grid are significantly different from the reference. The white bars are not significantly different from the reference.